In continuous ink jet printers of the type employing a plurality of drop streams, the natural tendency for ink streams (issuing from an array of orifices) to break up into droplets is synchronized by imposing waveform energy of a preselected frequency (one that provides a wavelength over a break-up threshold). This forms streams of uniformly spaced ink droplets which can be selectively charged at the break-up point of the ink stream filament and then deflected to a catch (or print) trajectory.
One problem in attaining high quality continuous ink jet printing is to assure (in addition to uniform drop size and spacing) that the drop break-up points of all jet streams occur within a given charging "window," i.e. a length range that extends along the drop stream path past the charge electrodes array. In forming ink jet arrays of substantial lengths, e.g. 6 inches or more, a number of problems evolve in attempting to achieve break-up of all jet streams within the charge window. First, the preferred mode of stimulation for long arrays is by traveling wave vibration of the orifice plate, which in itself introduces variations in the drop break-off point along the array length. Second, the traveling wave is reduced in amplitude as it moves from the point of vibrating contact (usually at one end of the orifice array) along the length of the orifice plate. A lower amplitude in the wave at a given orifice causes the ink stream filament (between that orifice and its break-up point) to lengthen. Third, reflected or second order vibration waves can cause additional non-uniformity, e.g. resulting in cuspings of break-off points along the length of the orifice array.
U.S. Pat. No. 3,882,508 provides good additional explanation about the second and third above-mentioned difficulties in achieving break-off point uniformity. The disclosure of the U.S. Pat. No. 3,882,508 also teaches that the reduction of wave amplitude along the length of the orifice array can be decreased by tapering the width of the effective vibrational area of the orifice plate, from a wider dimension at the point of vibration application to a narrower dimension at the opposite end of the orifice plate. To minimize reflected wave action, acoustic dampers can be provided at the ends of the orifice arrays (see the U.S. Pat. No. 3,882,508 disclosure) or a sharply narrowed width can be constructed at the end of the effective vibrational area of the orifice plate (see U.S. Pat. No. 4,110,759).
While the foregoing techniques are highly useful, they have not functioned well at longer array lengths (e.g., over 10.5"); and there are various applications where wider printing array capabilities would be highly useful (e.g. in newspaper printing, computer output printing and magazine signature printing).